DOKK / manpages / debian 10 / nbdkit / nbdkit-error-filter.1.en
nbdkit-error-filter(1) NBDKIT nbdkit-error-filter(1)

nbdkit-error-filter - inject errors for testing clients

 nbdkit --filter=error PLUGIN
     [error=EPERM|EIO|ENOMEM|EINVAL|ENOSPC|ESHUTDOWN]
     [error-rate=10%|0.1]
     [error-file=/tmp/inject]
     [error-pread=...] [error-pread-rate=...] [error-pread-file=...]
     [error-pwrite=...] [error-pwrite-rate=...] [error-pwrite-file=...]
     [error-trim=...] [error-trim-rate=...] [error-trim-file=...]
     [error-zero=...] [error-zero-rate=...] [error-zero-file=...]

"nbdkit-error-filter" is an nbdkit filter that injects random errors into replies from the server. This is used for testing that NBD clients can handle errors.

All parameters are optional, but you should usually specify one of the "error-rate" or "error-*-rate" parameters, otherwise this filter will do nothing.

Inject a low rate of errors randomly into the connection:

 nbdkit --filter=error file disk.img error-rate=1%

Reading and trimming requests will be successful, but all writes and zeroing will return "No space left on device":

 nbdkit --filter=error file disk.img \
                            error=ENOSPC \
                            error-pwrite-rate=100% \
                            error-zero-rate=100%

To make all connections fail hard 60 seconds after the server is started, use:

 rm -f /tmp/inject
 nbdkit --filter=error file disk.img \
                            error-rate=100% \
                            error-file=/tmp/inject
 sleep 60; touch /tmp/inject

When a random error is injected, you can select which one from the range of possible NBD errors (the NBD protocol only supports a limited range of error codes).

This parameter is optional and the default is "EIO" ("Input/output error").

The rate of injected errors per NBD request. This can be expressed as either a percentage between "0%" and "100%" or as a probability between 0 and 1. If "0%" or 0 is used then no errors are ever injected, and if "100%" or 1 is used then all requests return errors.

This parameter is optional and the default is "0%". Unless you set this, the filter will do nothing.

Errors will only be injected when FILENAME exists. (Note you must also specify the "error-rate").

You can use this for fine-grained control over when to inject errors, for example if you want to trigger an error at an exact moment during a test, arrange for this file to be created at the appropriate time. Or conversely to test error recovery in a client, create the file initially, and then delete it to check the client can recover.

This parameter is optional.

Same as "error", "error-rate" and "error-file" but only apply the settings to NBD pread requests.
Same as "error", "error-rate" and "error-file" but only apply the settings to NBD pwrite requests.
Same as "error", "error-rate" and "error-file" but only apply the settings to NBD trim requests.
Same as "error", "error-rate" and "error-file" but only apply the settings to NBD zero requests.

If you are looking at the debugging output (using "nbdkit -f -v") then you may see peculiar "errors" appearing when using this filter, for example:

 nbdkit: file.9: debug: error: pread count=1024 offset=0 flags=0x0

In fact these are not errors, nbdkit core is simply printing the name of the filter which happens to be "error". When this filter injects an error you will see something like:

 nbdkit: file.4: error: injecting ENOSPC error into pwrite

nbdkit(1), nbdkit-file-plugin(1), nbdkit-full-plugin(1), nbdkit-filter(3).

Richard W.M. Jones

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2019-01-26 nbdkit-1.10.3